It is known, in the prior art, to use various types of couplings to connect an input shaft to an output shaft to supply power from a prime mover to a load. Frequently the shafts are "locked" together in a manner such that torsional vibrations or shocks on either the input or output shaft are transmitted to the other shaft, many times with amplification, as well as to other parts of the apparatus. These vibrations or shocks may be caused by power surges, misfires and from sudden changes in demand load.
In the acceleration and deceleration of a given load, for example, short-term discontinuities of the energy flow, including reverse direction flow, may occur and this may result in such objectionable conditions as bumps or jerks or even cause harm to the equipment or stalling of the prime mover. This is particularly true in systems where a constantly or already running prime mover picks up a load when a clutch in the power train is actuated. Turning on an automobile air conditioner, for example, clutches in a heavy load, the compressor, in an already running power train which may be at a great variety of power conditions. Similarly "locking up" the torque convertor of an automatic transmission when cruising conditions are attained is a situation where load and input may be momentarily mismatched depending on the amount of hydraulic slip at the instant of engagement. In all of these systems, and others, troublesome vibrations or shocks may occur and with them inherent problems in the operation of such systems.
It, accordingly, is desirable to provide lock-up shafts with a cushioning device so that torsional vibrations or shocks are largely absorbed and not substantially transmitted from one shaft to the other. For example, in automotive vehicles that make use of an automatic transmission it may be desirable to include a lock-up clutch to couple the engine drive shaft directly to the transmission input shaft when the vehicle reaches a certain speed. Its purpose is to eliminate fuel losses related to torque converter slip. The shocks ordinarily occur during lock-up. Further, if the shafts are rigidly locked by this clutch, torsional vibrations or shocks on either shaft are transmitted to the other, as well as to the rest of the vehicle and its occupants. A torque cushioning device in series with the clutch is therefore desirable. Such a torque cushion must handle full engine torque, and any fractional part thereof, plus and minus the torsional vibrations derived from cyclic engine firing and other changes in demand load by the wheels. The softer the cushion the lower will be its natural frequency, and the better it will be for shock and vibration damping.
It, therefore, has become standard practice in the prior art, to incorporate some form of cushioning coupling in shaft lock-up systems to take up the initial load and to damp out bumps in operation. As an example, compression springs have been used for the torque cushioning portion of a lock-up clutch in an automotive vehicle, but their very presence, i.e., the space they occupy, plus their necessary loading elements, severely limits the amount of differential rotation permitted between the two shafts. Such systems are hard cushions with correspondingly high natural frequencies of vibration and, therefore, they perform poorly in response to sudden power surges and do little toward the damping of external vibrations. The basic problem remained unsolved.
As a further solution to this problem, it has been suggested, in the prior art, to use flexible couplings to connect the shafts together. In one approach, pins or rollers connected to one shaft are rotated in a circle inside a preformed noncircular flexible member connected to the other shaft to transfer torque; in another widely used approach pins connected to one shaft are moved relative to another shaft to stretch a flexible belt trained about the pins to couple the shafts, and to transfer torque from one shaft to the other. Typically in this latter coupling there are two sets of pins, one set is connected to a disc connected to one shaft and the other set to a disc connected to the other shaft, so that rotation of either shaft moves the pins connected to that shaft relative to the pins on the other shaft to place the required tension on the flexible belt to transfer torque to the other shaft. Prior to this invention, however, the art had not suggested the mounting of these pins eccentrically on planet gears which when rotated would move the pins in an arc toward or away from the shaft centerlines to place the required compression or tension on a flexible member (belt or spring) interconnecting such pins to transfer torque between shafts.
A typical coupling device or torque transmitter using a flexible belt trained about pins or rollers connected to two shafts is shown in copending U.S. patent application Ser. No. 013,193, filed Feb. 16, 1979 now U.S. Pat. No. 4,266,408. Such device essentially comprises a hub member and rim member, one of which is connected to an output shaft, and the other to an input shaft. The hub member has at least two hub rollers mounted on it, and the rim member, of larger diameter, is provided with a plurality of rim rollers. The hub and rim members are operatively connected by a flexible belt of an oriented copolyetherester elastomer trained over hub and rim rollers. This belt is capable of being stretched by up to about 60% of its original length upon application of force to either shaft to permit relative rotation of the hub member with respect to the rim member so that torque is transferred from one shaft to the other through such belt.
In this device, the rollers are fixed to the hub member and to the rim member and do not move radially with respect to the shaft centerlines; instead the belt is stretched by the circular movement of the rollers on one disc relative to the rollers on the other disc. While this is an effective way to transfer torque, it, nonetheless, places great stress on the belt, primarily due to the high degree of wrap as the belt is trained around the rollers on the hub member and rim member, which preferably are positioned so as to form modified triangular arrangements in their neutral or at rest positions. This motion, in time, tends to limit belt life due to reverse bending which can cause premature delaminations of the belt layers; additionally the requirement that the rollers be placed on both discs requires greater working space and this places spatial and rotatioal limits on the use of such coupling.
Another typical coupling for shafts using two sets of pins is shown in U.S. Pat. No. 643,081 to Bullock, patented Feb. 6, 1900. In this coupling, one shaft is rigidly secured to a first disc and the other shaft to a second disc and each of these discs has pins mounted thereon about which a flexible belt is trained. The pins on one of the discs are manually adjustable radially in the disc in a manner so as to tighten the belt or vary the tension thereof because in practice it would be inconvenient to place the belt upon the pins so as to be sufficiently taut for use. The radial adjustment is provided to give the belt the required initial tension after it has been placed on such pins. This is accomplished by rotating the pins in a large aperture in the disc, one way or the other, with the result of moving their projecting ends radially inward or away from the adjacent pins on the other disc, to take up the slack in the belt in an obvious manner. The pins are then locked in place using screws which pass through the heads of the pins to lock such pins from rotation.
A shaft coupler of the prior art using a preformed flexible member is shown in U.S. Pat. No. 3,877,259 to Bishop. In this device for coupling a drive shaft and a driven shaft, a polygonally shaped or noncircular coupling element in the form of a plurality of yieldable beam member is used. Such element is adapted to be supported by and to rotate with the driven shaft. The inner surfaces of the yieldable beam members define a noncircular opening for accommodating a plurality of rotary coupling members, as for example a plurality of rollers. These rollers revolve as a unit with and about the axis of the drive shaft and are maintained in engagement with the inner surface area of the yieldable beam members whereby flexibly to couple the shafts together and drive the driven shaft. In this device the rollers which create the necessary forces in the yieldable members to drive the driven shaft rotate in a circular path around the centerline of the end-to-end shafts; they do not move radially with respect to such shaft.
A problem with the above teachings, and with the other known art, is that there is no suggestion of a relatively simple way to change the length of a flexible belt or spring, by moving a single set of pins to which the belt is connected relative to the centerlines of the shafts; that is, in a smooth arc either toward or away from such centerlines to stretch the belt so that it serves to lock-up such shafts in a positive, progressive manner, and using a positive and reversible drive train. By so doing, lock-up may be achieved in a limited space in an effective manner while absorbing the energy pulses between the shafts.
The oscillation damping coupling of this invention is characterized by simplicity, low cost, ease of assembly, low friction, low natural frequency as compared to metallic compression spring systems, improved cushioning and vibration damping capability, large angular displacement repeatable performance and smooth operation over a long useful life. The configuration is dynamically balanced over the entire range of operation. It is particularly amenable to a large range of design variations to suit the parameters of specific applications.
This invention solves the problems of the prior art, or improves on the solutions offered by that art, or gives a viable alternative to the couplings taught by such art, by interconnecting a single set of pins eccentrically mounted on planet gears with a flexible member and by moving these pins either away from or toward the centerline of the shafts, in an arc, using a positive drive gradually to create sufficient torque to couple the shafts together.
Accordingly, prior to this invention, there was a need for a simple device to create adequate forces in a flexible belt or spring using the relative motion of the shafts to create a low-friction positive drive system for moving belt supporting the pins away from or toward the centerlines of the shafts to bring about this torque force. This invention, in filling this need, and solving the problems inherent in the prior art provides such an apparatus and, in doing so, gives the shaft coupling art improvements heretofore not known to such art.